Device for testing the compression characteristics of sheet metals



Sept; .4, 1945. D. s. WOLFORD ETAAL DEVICE FOR TESTING THE COMPRESSION CHARACTERISTICS OF SHEET METALS Filed May 6. 1943 :1 won M I 001v 5 WOL FORD Fl 6 Z Y MAW) L4 7001?- Patented Sept. 4, 1945 UNITED STATES PATENT. OFFICE 2,ss4,4 11 DEVICE FOR TESTING THE COMBRESSION CHARACTERISTIC s F SHEETMETALS Application May 6, 1943, Serial180.48%850 9 Claims.

With the increasing useof high-strength,.lightgauge sheet metal in various constructions, more adequate meansior testingthe physical characterlstics of such materials are needed. In the past, it has, ,been custcmaryqto design structural shapes of sheet .metalon the basis of the tensile strength tests. ..It.is, howevennowgenerally recoen'ized that tensile-tests are 'notalone adequate for. the purpose. }for ,the. jreason that .such structures almost invariably fail in compression rather than in tension. While insufficient data exists to make it proper .tosaythat the compression characteristics of sheet metal bearno necessary relationship .totheir tensile characteristics, it is propel-to saythat tensile strength tests on highstrength, light-gauge .sheet metal are not reliable guides to the behavior of the same materials under compression. 1

The compression testing or sheet metals has largely been neglected until recently, though some compression methods have.been developed. All of thesemethods possessinherent disadvantages; whereas the increasing use of thin sheet materials in aircraft and other fieldsof manufacture is making imperative the development of mechanism and procedure whereby the compression properties oi these materials can bedetermined quickly and inexpensively.

The pack method, which has been proposed by the National Bureau of Standards, tends to be costly .and'time-ccnsuming, since it involves the necessity of lining up the test piece with a relatively large number of other pieces of .difierent dimensionin forming a pack for test purposes, and bracing it laterally by a large number of individually adjusted supporting rods.

Franks and Binder have proposed a cylinder, method, but vthis again involves .difliculties and uncertainty because anunknown amount of strain is likely .to be introduced into the .test materialin the .formingor rolling operation by which it is curved intoa cylinder. Unknown factors are also likely to be introduced in any seam formed in the-cylinder. Moreover timeand skill are required to prepare the sample.

Montgomery and Templin-have devised a single strip .test wherein thestriP-is supported in a ji orthe like by means of tiny roller bearings at each-sside-of it. These bearings are set on 0.1 inch centersacross thesamp a ong almost the entire length chit. .It will be understood that this rcquiresanelaborate iig iorsupporting the rollersandconsiderabletime for-assembly. Moreoverpit hasfc'ertaill physical limitations. The

spacing or the rollers limits the minimum cause ofmaterialthat eanbe tested. ltiwill be under stood that the}support aiforded'by-the. rollers'i limited to wane-savann see etins ml with sel e ee 9- cen s the 5 thicknessoLmateri ,m u cambetested-islim ited 'to.. appr9;dmat oggin. If thinner shot material fits :isudeutviistabuclslel h than se m e fir 1 -1. thauearatwcmpl a 10 the leu thofithesm lewith respechtmthe lengt of t dis has. beenrsucha itoin pxide al aram of onl -05 ueati uegendu Miam 64 1. we the-lie. there beingmozcl aranceat tthe other; en of-the jig." Thislim tsxherm'axlmum straimwhic canbe:imposed:omthesamplmtofsuchwnexter thatirequentlysufiicient datazcannct beobtaine on high strengthu rni-iteririlsL-: Itchas also bee noted that ithe tellers. ibemsfllus a'tend :tofinder the sample to suchcan extent that some-apnoea taintyu's introduced. 1

It is a, general objector our inventionto obvia' the difficulties which have :iust ibeen mentio'ne It is ourobiect-to brovide'a-struetur whichw accept an individual sample and hold iitin .su: a waythat a true compression test-maybe ma on it. It is our object'toaccomplishithis witl out-the necessity of accurate or elabora'te' adjus ment, and also without the necessity'cf comp; cated or elaborate apparatus. It is an object off bur'invention to provide holder for a compression test sample in which 11 is made offiat"bearing bodies'ashereinafter d scribed, aud'in which supporting means ls pr .vided for ejholder insuch fashion as to faci we h n ert on senescence Sample wi proper. and accurate clearance, which clearar occurs Iatboth ,endspf Lthe holder, and is s\ ficient tor thel complete testing of high-strene materials.

It isa b ect o jpurim utim t Pr d devlce whlchcan be used";w ith' the standard co pressometer, such as' is f-set Tgrth v in Bulletin 1 of the Baldwin-SOilthWgIk Company. and .8 19 in F refiz of that bulletin.

It is an object .or puriinventionuto providl device which has anabsolute minimum of pa and can be used by inexperienced operators making very rapid ,but none the-less .accu'r compression tests.

These and otherobiects of our invention, .wh will be. set .forth hereinafter or. .will .be .appar to one skilled inthe art upon readingthese spr fications. .weaccomplish by-that certain constr M tion;and arrangement of Parts of whichwe sl nowhescribe anieaemplaryembodiment. Rel

ence is made to the accompanying drawing in which:

Figure 1 is a plan view of our jig and a positioning device therefor.

for the usual sheet gauges employed for constructional purposes,

A bore 2 is formed through the body I from end to end. For a sample having a 12 in. width,

Figure 2 is an elevational view of the same elethe bore may initially be formed With a /64 drillmente 4 One sidev of the bore isflattened, as .at 3, to conwhilethere i no limitation nthe physical form to the face of the'sample. The width of dimensions of our device, as will be apparent the flattened portion is the same as the width hereinafter, in its exemplary embodiment, it is of the drilled hole, namely, .525 in. thus providdesigned to accept a sample which is 2 in. long i s adequate a n e or ed ewise spreadi of and A in. wide and, of course of" variable thickthe sample during the test. For the sake of balness as determined by t gauge of th h t ance, the flat'face 3 is preferably so located that from which t samples h; gives u a for the average thickness of sample, the sample t t specimen hi i comparable'jq-jhestandwill be located in the jig with its center plane ard sh t t il t t specimen u d in a c da c substantially coinciding with an axial plane of the with the known A. -S. T. M. standard. J' 1 w have found t t compression t ts may b Within thebore, we place a clamping member made upon a sample simply clamped betw'een flat' in he form, preferably, o a half-round P e surfaces conforming t it sides d it -t of tool steel havingn flat face 5 to contact the specimen projecting at one or both ends of the pp te face of the sample- F r h e rtion of jig which presents those flat surfaces. Former lampin pr s r provide apa of t c ews. workers have apparently proceeded on the as- 5 in ee into lateral bores in t bed-3. sumption that it was necessary to relieve friction The ends of e t Screws preferably at the sides of the sample either by providing no r d a h wn in Figure 2, and recessestl and support at all as in the cylinder method, or by 9 a e r ra y drilled i h arcuate a of providing anti-frictional roller supports as in the ec ampi member, o that he s c w Montgomery'and Templln method, or by more or may serve to retain the clamp m mb .4 w less elastically supporting the test sample in the in bore'dilling the insertion'and removal b midst of a pack of similar pieces which will be p t before y amp p essure has compressed along with the-sample and distorted been eXeIted-v ample i indicatedin thefig' r'es to the same extent. -W e have found that" this is at l I not the case; buton' the ontraryflt is possible-to siiice it is iiesiled t0 have the Sample .D osupport thesample-*betweeniha'rd, non-yielding i t t ends of the lie. and since if this is supporting surfaces sufhciently to prevent-benddone; the jig Wiii not'iesit flatly upoii the bed m without encountering any fri ti al m mon platell'l "or the pressin which'thecompression ties." Test results obtained by our procedure are e is to beICORdUCted; p ovide a jig. holde equivalentto test results otherwise obtained and which in its operation not nl s e l quite as'accurate. Whether an'increase'in thickg upright during loading 'unl ine. ness of the test piece occurs during compressio but also facilitates the proper insertion of the and to what extent has 'notbeen. ascertained by 40 sample in i i usy-but such an increased thickness if'it occurs This means comprises a ring Q Somewhat does not affect the accuracy-of our results. It is large! in internal diameter shap than the our general practice -tocoat either-the side faces body T e H s provided with set screws of t sample. the .clamping fa f the jig l2, l3 and I4, threaded into lateral projections with a high-pressure grease as a precautionary 4 in the ring, and engaging e SSeS, as at IS in the measure, b t results appeapfio Show t t t is body I. Both the set screws andthe recesses are not necessary; preferably tapered for accurate location, and are o jig may be made in a variety f m so positioned that when the ring is held to the tions, and in particular it is not necessary that body i by the Set W it Will pDO the body the jig body. he machmedpr f d fr a SlL above a surface upon which the ring rests by, the tary piece of metal. 'It can be made from parts distance f in the e p y e odime tbolted or otherwise fastened together. The memwith the set screws 6 and 7 in the released D bers presenting t flat clampjng surfaces may tion, then, the sample I0 may be inserted between both be mademovable andadjustable if desired. the faces 3 and 5 of e c pin members and Our jig, in itspreferred embodiment, comprises passed downwardly until it rests against the supa, y ndrical orothershaped b dy |,.pref rab1 porting surface. Its lower clearance will then be of tool steel or its equivalent. It is accurateas to -0 a assuming h sample t 'be accurate length so that when a test piece is placed in a i length. its pper clear nce Will be the same. bore formed within it, :the test piecewill project The Surface p n which the ring an j rest at one .or both ends by the desired amount of so will u y be the platen of the pr but it may clearance. W pr f r a' j ti t b th ends be some other flat/surface. With the sample in because thisfgivesa greatercombined ortotal position, the set screws 6 and 'l are tightened. clearance, and permits the obtaining of complete This is merely done y handh Clamping l data on high-strengthmaterials where a clearsure should besubstantially uniform, i. e.) one of ance at one end ,may not be sufficientforthe pur- 05 the set screws should not deliberately be tightpose. For 2 i samples f ordinary sheet gauges ened tighter'than the other; but the 'degree of throughout a wid range a projectionoj th pressure is not important as respects the ac ple .050 in. at each end of the jig is sufiicient for curacy o the test; It ishot desired toiciamvp the testing purposes without giving rise to danger of sample under any very great pressure, and a bendin Over of the proje ting sample ends. It tighteni wi h t e rs is s fiicient; will be understood by the skilledworker that, If the po i io i o the sa p e h sn'ot been depending somewhat on the material being tested, accomplished while the j and ring are positioned the gauge of the sample will roughly determine on the platen of the press, they are'next trans." how far it may project; but, as indicated, a proferred to the press, and the ram is brought down i jection of .050 in. at each end of the jig is feasible gently against the upper projecting end or the-;

sample. It isdesired at this point merely to clamp =the sampleendw-ise between the press, platens with sufficient force to maintain the upright position of; the -jig; When this -is accomplished, the set screws-12,43 and -l4.,are loosened so that the jig .isfreed from the ring ;I I which, thereafter, performs no function during the test. During the test zany movement-of the jig body i produced by end-wise,-:compres sion of the sample will thus produce a movement of the jig body relative to the ring II from which it is now free. Where the thickness of the ring is such as to bring it into the plane of the lower set screw 7, it is relieved, as at I 6, to permit such sliding movement.

The nature of the compression test itself is known and need not be detailed here. We have already indicated a type of compressometer preferred for rapid testing; but it will be understood that other types may be used. For example, the Huggenberger extensometer can be attached to the edges of the test sample. To permit this, windows are provided in the body of the jig so that the edges of the sample are exposed for suitable contact with the measuring points of the extensometer.

While we have indicated the body I as a cylindrical body, and while it is most conveniently formed in this way, it may have other configurations, as will be evident. It enters into the testing procedure merely as a means for positioning the test sample in the test position, and for maintaining it against flexing or bending during the compression step which forms a part of the test.

Modifications may be made in our invention without departing from the spirit of it. Having thus described our invention, what we claim as i new and desire to secure by Letters Patent is:

l. A jig for a sample to be subjected to compression tests, said jig comprising a metal body having a hollow therein with means to present a flat longitudinal face, a metal part located in said 5 hollow and having a matching flat; face, means i for urging the metal part under pressure toward the first mentioned 2 can be engaged and clamped between the flat fiat face so that a test sample faces, the length of the body being so proportioned to a. given length of test sample as to provide for the extension of the sample through the said body and the projection therefrom at both ends, and means to support said body above a flat surface such as the platen of a press with said flat faces normal thereto, and with said body so spaced from said surface as to gauge the projection of said sample from said body.

2. A jig for a sample to be subjected to compression tests, said jig comprising a metal body having a hollow-therein with means to present a flat longitudinal face, a second metal part located in said hollow and having a matching flat face, and means for urging the second member under pressure toward the first mentioned fiat face so that a test sample can be engaged and clamped between the flat faces, the length of the body being so proportioned to a given length of test sample as to provide for the extension of the sample through the said body and the projection therefrom at; both ends, in combination with a detachable support comprising a portion to embrace an end of said body and means on said portion to engage said body and hold it at a fixed distance above a surface on which said support rests so that said support in coaction with a surface on which it rests may determine the downward projection of a test sample below said first mentioned body.

3. A jig formaking compressiontests, having .a body with alongitudinal bore, said bore having a flattenedface, a metal piece of substantially the same length as said body :and also-'having'a flattened face, located in',.said -bore,"j-set screws threaded intolateral perforations, gsaid body and engaging said metal piece so that a test sample may be clamped between said flat faces so as to lie substantially along the .axis of.- said body, said body having a length apportioned to a given length of test sample so that the said sample can extend through said body and project therebeyond at; both ends, in combination with releasable means for supporting said jig a distance above a flat surface suflicient to gauge the projection of said sample equally at both ends whereby a sample may be engaged in said jig,

the ends of said sample engaged by the platens of a press, and the releasable means released, leaving the sample supporting the jig.

4. The structure of claim 1, wherein said supporting means, comprises an embracing member with an opening larger than said body, set screws threaded laterally through said member, depressions on said body in which the ends of said set screws may engage so that said member can support said body above a fiat surface upon which said member rests a distance equal to the desired downward projection of said test sample from said body.

5. The structure claimed in claim 3 wherein said body is 1.9 in. in length, and wherein said releasable means is capable of supporting said body accurately .05 in. above a fiat surface on which said releasable means rests.

6. The structure claimed in claim 3 wherein said body is 1.9 in. in length, and wherein said releasable means is capable of supporting said body accurately .05 in. above a flat surface on which said releasable means rests, the width of the fiat face of said bore in said cylindrical body being approximately .525 in., and the width of the fiat face on said metal piece being approximately .50 in., the said jig accepting a 2 in. test sample with a projection of .05 at each end of the Jlg.

7. In combination for the purpose described, clamping means for a flat elongated compression test sample, said clamping means comprising a body and a movable clamping element both having fiat faces for engaging said sample, and means for causing said body and element to exert clamping pressure sidewise on said sample, and a removable fixture for holding said clamping means a fixed distance above a flat surface so that a test sample may be positioned in said clamping means accurately with a predetermined projection at each end thereof.

8. A process of performing compression tests upon elongated test samples of sheet material which comprises providing a jig having flat clamping faces and pressure exerting means, providin a sample of sufficient length to extend through said jig and project at both ends by a distance substantially equivalent to .05 in. in 2.0 in. overall length, positioning and clamping said sample in said jig with the same projection at each end, and subjecting the sample to compression while clamped in said jig under circumstances in which the sample itself, by engaging the opposed platens of a press, supports the jig between said platens.

9. A process of performing compression tests upon elongated samples of sheet material which comprises providing a jig having flat clamping faces and pressure exerting means, providing a sample of sufficient length to extend through said jig and project at both ends a distance insuflicient to permit bending under compressive forces applied in the direction of the length of the sample, positioning and clamping said sample in said jig with the sample projecting at each end, placing and holding the jig between the platens of a press in such a way as to cause the sample to extend normal to said platens, bringing said platens into engagement with the ends of said sample, then permitting the jig to be supported between the platens solely by means of the sample, and thereafter applying further compressive force to the sample by means of the platens.

DON S. WOLFORD.

HARRY LA TOUR. 

